John Dimes

Bio: John Dimes is an academic researcher from International Crops Research Institute for the Semi-Arid Tropics. The author has contributed to research in topics: Agriculture & Sorghum. The author has an hindex of 16, co-authored 24 publications receiving 1631 citations. Previous affiliations of John Dimes include Department of Employment, Economic Development and Innovation & Wageningen University and Research Centre.

Micro-dosing as a pathway to Africa’s Green Revolution: evidence from broad-scale on-farm trials

Abstract: Next to drought, poor soil fertility is the single biggest cause of hunger in Africa. ICRISAT-Zimbabwe has been working for the past 10 years to encourage small-scale farmers to increase inorganic fertiliser use as the first step towards Africa’s own Green Revolution. The program of work is founded on promoting small quantities of inorganic nitrogen (N) fertiliser (micro-dosing) in drought-prone cropping regions. Results from initial on-farm trials showed that smallholder farmers could increase their yields by 30–100% through application of micro doses, as little as 10 kg Nitrogen ha−1. The question remained whether these results could be replicated across much larger numbers of farmers. Wide scale testing of the micro-dosing (17 kg Nitrogen ha−1) concept was initiated in 2003/2004, across multiple locations in southern Zimbabwe through relief and recovery programs. Each year more than 160,000 low resourced households received at least 25 kg of nitrogen fertiliser and a simple flyer in the vernacular explaining how to apply the fertiliser to a cereal crop. This distribution was accompanied by a series of simple paired plot demonstration with or without fertiliser, hosted by farmers selected by the community, where trainings were carried out and detailed labour and crop records were kept. Over a 3 year period more than 2,000 paired-plot trials were established and quality data collected from more than 1,200. In addition, experimentation to derive N response curves of maize (Zea mays L.), sorghum (Sorghum bicolor (L.) Moench) and pearl millet (Pennisetum glaucum (L.) R.Br.) in these environments under farmer management was conducted. The results consistently showed that micro-dosing (17 kg Nitrogen ha−1) with nitrogen fertiliser can increase grain yields by 30–50% across a broad spectrum of soil, farmer management and seasonal climate conditions. In order for a household to make a profit, farmers needed to obtain between 4 and 7 kg of grain for every kg of N applied depending on season. In fact farmers commonly obtained 15–45 kg of grain per kg of N input. The result provides strong evidence that lack of N, rather than lack of rainfall, is the primary constraint to cereal crop yields and that micro-dosing has the potential for broad-scale impact on improving food security in these drought prone regions.

Farming with current and future climate risk: Advancing a 'Hypothesis of Hope' for rainfed agriculture in the semi-arid tropics

Abstract: Climate change predictions point to a wanner world within the next 50 years, a trend that is increasingly being supported by 'on-the-ground' measurements. However, the impact of rising temperatures on rainfall distribution patterns in the semi-arid tropics (SAT) of Africa and Asia remains far less certain. During 2008, ICRISA T's crop modelers, GIS experts, crop physiologists and plant breeders met in Hyderabad, India for one week. Using a range of weather data driven tools, they initiated research to test the hypothesis that "in the medium term (2010-2050). ICRISAT is well placed to help farmers mitigate the challenges and exploit the opportunities that are posed by climate change through: (i) the application of existing knowledge on crop. soil and water management innovations, and (ii) the re-deployment and re-targeting of the existing germ plasm of its mandate crops." Rather than selecting specific climate change scenarios, we chose to undertake a 'sensitivity-based' analysis in which we looked at the impact of a factorial combination of climate change of5 different temperature increases (I, 2, 3, 4 and 5°C) and 3 different percentage changes in seasonal rainfall (0%, + I 0% and -10%) and compared the outputs with a 'control' of the current climate at each location for which the analyses was undertaken. We undertook three types of analyses. Firstly, we looked at the implication of these climate change combinations for changes in the length of growing period (LGP) and how they might effect the global distribution and extent of the SAT. Secondly, we examined in some detail how these scenarios would impact on crop production (millet, sorghum, groundnut and pigeonpea) in eastern, southern and western Africa and in India. We also looked, albeit to a lesser extent, at the potential 'fertilizer effect' of enhanced CO2 levels on crop production. Finally, we examined the potential of improved production practices and better adapted germplasm to mitigate the impact of climate change.

Rainwater harvesting to enhance water productivity of rainfed agriculture in the semi-arid Zimbabwe

Abstract: Zimbabwe’s poor are predominantly located in the semi-arid regions and rely on rainfed agriculture for their subsistence. Decline in productivity, scarcity of arable land, irrigation expansion limitations, erratic rainfall and frequent dry spells, among others cause food scarcity. The challenge faced by small-scale farmers is to enhance water productivity of rainfed agriculture by mitigating intra-seasonal dry spells (ISDS) through the adoption of new technologies such as rainwater harvesting (RWH). The paper analyses the agro-hydrological functions of RWH and assesses its impacts (at field scale) on the crop yield gap as well as the Transpirational Water Productivity (WPT). The survey in six districts of the semi-arid Zimbabwe suggests that three parameters (water source, primary use and storage capacity) can help differentiate storage-type-RWH systems from “conventional dams”. The Agricultural Production Simulator Model (APSIM) was used to simulate seven different treatments (Control, RWH, Manure, Manure + RWH, Inorganic Nitrogen and Inorganic Nitrogen + RWH) for 30 years on alfisol deep sand, assuming no fertiliser carry over effect from season to season. The combined use of inorganic fertiliser and RWH is the only treatment that closes the yield gap. Supplemental irrigation alone not only reduces the risks of complete crop failure (from 20% down to 7% on average) for all the treatments but also enhances WPT (from 1.75 kg m−3 up to 2.3 kg m−3 on average) by mitigating ISDS

Productivity and residual benefits of grain legumes to sorghum under semi-arid conditions in southwestern Zimbabwe

Abstract: The productivity and residual benefits of four grain legumes to sorghum (Sorghum bicolor) grown in rotation were measured under semi-arid conditions over three cropping seasons. Two varieties of each of the grain legumes; cowpea (Vigna unguiculata); groundnut (Arachis hypogaea); pigeon pea (Cajanus cajan); Bambara groundnut (Vigna subterranea), and sorghum were grown during the first season. The same experiment was implemented three times in different, but adjacent fields that had similar soil types. At the end of the season the original plots were split in two and residues were either removed or incorporated into the subplots. The following season sorghum was planted in all subplots. In 2002/03 (314 mm rainfall) cowpeas produced the largest dry grain yield (0.98 and 1.36 t ha−1) among the legumes. During the wettest year (2003/04, 650 mm rainfall) groundnut had the highest yields (0.76 to 1.02 t ha−1). In 2004/05 (301 mm rainfall) most legume yields were less than 0.5 t ha−1, except for pigeon pea. Estimates of % N from N2-fixation from the legumes were 15–50% (2002/03), 16–61% (2003/04) and 29–83% (2004/05). Soil water changes during the legume growth cycle were proportional to varietal differences in total legume biomass. Sorghum grain yield after legumes reached up to 1.62 t ha−1 in 2003/04 compared with 0.42 t ha−1 when following sorghum. In 2004/05, sorghum yields after legumes were also higher (up to 1.26 t ha−1) than sorghum after sorghum. Incorporation of crop residues had no significant effect on sorghum yield. Beneficial effect of legumes on yields of the subsequent sorghum crop were more readily explained by improvements in soil nitrogen supply than by the small observed changes in soil water relations. Our results demonstrate clear potential benefits for increasing grain legume cultivation in semi-arid environments through the use of improved germplasm, which also gave substantial increases in subsequent sorghum productivity (up 200% in a wet season and 30–100% in a dry season), compared with an unfertilized sorghum crop following sorghum.

Global food demand and the sustainable intensification of agriculture

Abstract: Global food demand is increasing rapidly, as are the environmental impacts of agricultural expansion. Here, we project global demand for crop production in 2050 and evaluate the environmental impacts of alternative ways that this demand might be met. We find that per capita demand for crops, when measured as caloric or protein content of all crops combined, has been a similarly increasing function of per capita real income since 1960. This relationship forecasts a 100–110% increase in global crop demand from 2005 to 2050. Quantitative assessments show that the environmental impacts of meeting this demand depend on how global agriculture expands. If current trends of greater agricultural intensification in richer nations and greater land clearing (extensification) in poorer nations were to continue, ∼1 billion ha of land would be cleared globally by 2050, with CO2-C equivalent greenhouse gas emissions reaching ∼3 Gt y−1 and N use ∼250 Mt y−1 by then. In contrast, if 2050 crop demand was met by moderate intensification focused on existing croplands of underyielding nations, adaptation and transfer of high-yielding technologies to these croplands, and global technological improvements, our analyses forecast land clearing of only ∼0.2 billion ha, greenhouse gas emissions of ∼1 Gt y−1, and global N use of ∼225 Mt y−1. Efficient management practices could substantially lower nitrogen use. Attainment of high yields on existing croplands of underyielding nations is of great importance if global crop demand is to be met with minimal environmental impacts.

Recent patterns of crop yield growth and stagnation

Abstract: In the coming decades, continued population growth, rising meat and dairy consumption and expanding biofuel use will dramatically increase the pressure on global agriculture. Even as we face these future burdens, there have been scattered reports of yield stagnation in the world's major cereal crops, including maize, rice and wheat. Here we study data from ∼2.5 million census observations across the globe extending over the period 1961-2008. We examined the trends in crop yields for four key global crops: maize, rice, wheat and soybeans. Although yields continue to increase in many areas, we find that across 24-39% of maize-, rice-, wheat- and soybean-growing areas, yields either never improve, stagnate or collapse. This result underscores the challenge of meeting increasing global agricultural demands. New investments in underperforming regions, as well as strategies to continue increasing yields in the high-performing areas, are required.

Food security and food production systems

Abstract: Many definitions of food security exist, and these have been the subject of much debate. As early as 1992, Maxwell and Smith (1992) reviewed more than 180 items discussing concepts and definitions, and more definitions have been formulated since (DEFRA, 2006). Whereas many earlier definitions centered on food production, more recent definitions highlight access to food, in keeping with the 1996 World Food Summit definition (FAO, 1996) that food security is met when “all people, at all times, have physical and economic access to sufficient, safe, and nutritious food to meet their dietary needs and food preferences for an active and healthy life.” Worldwide attention on food access was given impetus by the food “price spike” in 2007–2008, triggered by a complex set of long- and short-term factors (FAO, 2009b; von Braun and Torero, 2009). FAO concluded, “provisional estimates show that, in 2007, 75 million more people were added to the total number of undernourished relative to 2003–05” (FAO, 2008); this is arguably a low-end estimate (Headey and Fan, 2010). More than enough food is currently produced per capita to feed the global population, yet about 870 million people remained hungry in the period from 2010 to 2012 (FAO et al., 2012). The questions for this chapter are how far climate and its change affect current food production systems and food security and the extent to which they will do so in the future (Figure 7-1).

Determinants of risk: Exposure and vulnerability

Abstract: Many climate change adaptation efforts aim to address the implications of potential changes in the frequency, intensity, and duration of weather and climate events that affect the risk of extreme impacts on human society That risk is determined not only by the climate and weather events (the hazards) but also by the exposure and vulnerability to these hazards Therefore, effective adaptation and disaster risk management strategies and practices also depend on a rigorous understanding of the dimensions of exposure and vulnerability, as well as a proper assessment of changes in those dimensions This chapter aims to provide that understanding and assessment, by further detailing the determinants of risk as presented in Chapter 1 The first sections of this chapter elucidate the concepts that are needed to define and understand risk, and show that risk originates from a combination of social processes and their interaction with the environment (Sections 22 and 23), and highlight the role of coping and adaptive capacities (Section 24) The following section (25) describes the different dimensions of vulnerability and exposure as well as trends therein Given that exposure and vulnerability are highly context-specific, this section is by definition limited to a general overview (a more quantitative perspective on trends is provided in Chapter 4) A methodological discussion (Section 26) of approaches to identify and assess risk provides indications of how the dimensions of exposure and vulnerability can be explored in specific contexts, such as adaptation planning, and the central role of risk perception and risk communication The chapter concludes with a cross-cutting discussion of risk accumulation and the nature of disasters